The present invention generally relates to the fabrication of gold circuit patterns on a substrate and, more specifically, to the production of fine-geometry gold circuit patterns using an environmentally safe chemical etching method and apparatus.
Gold circuit patterns may be formed on a semiconductor substrate using techniques which are generally known in the art. Typically, a layer of photoresist is deposited on a seed layer of gold. Ultraviolet light is shined on the photoresist layer through a mask to define circuit patterns. The ultraviolet light hardens the photoresist layers in areas defined by the mask. Gold plating is then performed to deposit 6 to 7 microns of gold on top of the exposed seed layer of gold. The hardened photoresist on top of the seed layer of gold is 2-3 microns deep. Next, the hardened photoresist is removed exposing the seed layer of gold below the hardened photoresist. Finally, gold etching is performed to remove a portion of the electroplated gold and the exposed seed layer of gold. The gold etchant chemical solution is generally potassium iodide (iodine) or cyanide based.
In the gold etching process, a substrate is typically processed for 40 to 60 seconds in an etching solution that was previously heated to 50.degree. C. The substrate is then inspected for bridging, etch rate, gold thickness, and coupler gap. The processing and inspection is repeated until all specifications are met (i.e., gap width, gold thickness, and cleanliness around boundary).
Iodine or cyanide based etching solutions are environmentally unsafe and require daily preparation by an operator. Gold reclaim requires that the post-etch solution has to be carefully labeled and filtered by an operator.
Etching gold with iodine and cyanide based solutions is generally limited to processing one or a small number of substrates at a time due to difficulty in controlling etch rate and uniformity. For example, when etching small geometric patterns, an operator must visually inspect the substrate during processing to minimize bridging. Further by way of example, to prevent over-etching, the operator must control the temperature of the etching solution to maintain constant etch rate. Bridging and over-etching both contribute to yield loss.
Accordingly, it is an object of the present invention to provide a novel etching apparatus for etching gold without using iodine or cyanide based chemicals.
It is another object of the present invention to provide a novel method of etching gold in which gold is etched using an iodine and cyanide free chemical.
It is yet another object of the present invention to provide a novel apparatus for manufacturing fine-geometric gold patterns using current flow.
It is still another object of the present invention to provide a novel solution for etching gold.
It is a further object of the present invention to provide a novel technique for etching gold using an environmentally safe etchant.
It is yet a further object of the present invention to provide a novel method and apparatus for maintaining a constant etching rate during gold circuit etching.
It is still a further object of the present invention to provide a novel apparatus and method for manufacturing gold circuit boards with increased lot size and reduced operator supervision.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.